Recovery of shale oil



Feb. 8, 1966 J. P. HAMILTON ETAL 3,233,663

RECOVERY OF SHALE OIL Filed Nov. 15. 1963 5 Sheets-Sheet l FIG-l- FRACTURING FLU) -O2 INJECTION FRACTURING H 7 FLUID 2 2! 7 22 I I5 I6 lZ I6 I5 CASING CASING OVER BURDEN OPEN-HOLE/ SHALE OIL ZONE BURNING ZONE OZINJECTION I? H] l3 FIG- IA. 28

. INVENTORS. SHALE OIL ZONE 2; JULIAN P.HAMILTON,

r' NICK P. PEET l3 1; BY

8, 1966 J. P. HAMILTON ETAL 3,233,668

RECOVERY OF SHALE OIL 3 Sheets-Sheet 2 Filed Nov. 15, 1963 EN 0 O T H WM VA H m. P N A L U J NICK P. PE'ET,

TTORNE Y.

1966 J. P. HAMILTON ETAL 3,233,668

RECOVERY OF SHALE OIL Filed Nov. 15, 1963 3 Sheets-Sheet I5 49 TO HYDROGENATION ATMOSPHERIC DISTILLATION H20,CO2,LT.HC. TOWER TO BOILER FuEL.

VACUUM DIST TOWER I 0 INJECTIONE SEPARATOR 34- H2O TO FRACTURING 5o FLUID 7"" ELECTROLYSIS 46 BOTTOMS TO BOILER FUEL FINES RETURN LINE I2 FIG. 4.

WSUPPLEMENTARY FUEL RETURN LINE "54 56 WW,- I CAVERN y HYDROGENATION Q: 55

cA'rALYsT-- I SHALE OIL/ I PRESSURE ZONE ELECTROLYSIS JJ. CHAMBER |2 -58 WATER AND ELECTROLYTE F G A INVENTORSI JULIAN P. HAMILTON,

NICK P. PEET, BY

TTORNEY.

United States Patent 3,233,668 RECOVERY OF SHALE OIL Julian P. Hamilton, Baytown, and Nick I. Peat,

Houston, Tex., assignors, by mesne assignments, to

Esso Production Research Company, Houston, Tex., a

corporation of Delaware Filed Nov. 15, 1963, Ser. No. 324,078 15 Claims. (Cl. 166-7) The present invention is directed to a method for the recovery of shale oil. More particularly, the invention is concerned with the recovery of shale oil from oil shale formations by in situ combustion operation. In its more specific aspects, the invention is directed to the recovery of shale oil by drilling wells into the oil shale formations.

The present invention may be briefly described as a method for recovering oil from a subsurface oil shale formation wherein a plurality of wells are drilled or provided in the shale oil formation. Thus, a first well opens into the lower portion of the formation and a second well opens into the formation adjacent the first well. A third well opens initially into the formation adjacent and between the first and second wells. The formation is fractured through the third well and thereafter free oxygen is injected into the fractured formation to support a combustion operation in the fractured formation. By burning the fractured formation, a cavern is formed therein and the free oxygen is injected at a sufficient velocity to form in the cavern a fluidized bed. In the lower portion of the cavern, a burning zone is provided and a retorting and cracking zone is provided in the upper portion of the cavern. Raw shale is fed into the fluidized bed and the cavern is enlarged by progressive upward caving of the cavern roof achieved by means of explosives, hydraulic fracturing, or other techniques. Shale oil and combustion products are formed in the cavern and are removed from the cavern through the second well.

It is contemplated in the practice of the present invention that a plurality of caverns will be formed in the shale oil formation with each cavern being formed around an oxygen injection well and having supporting wells for fracturing and for recovery of the products. By virtue of having a plurality of caverns which will be formed around wells drilled on centers a distance apart within the range from about 200 feet to about 1000 feet, with the caverns having diameters which may range ultimately from about 50 feet to about 500 feet, it is possible not only to recover shale oil from the oil shale formation in which the cavern is formed but also from the oil shale formation surrounding the caverns by virtue of heat being transferred from the caverns into the walls which causes retorting to take place in the walls; as a result, shale oil flows from the walls into the caverns and is cracked and vaporized for recovery with the shale oil and combustion products in the cavern.

In the practice of the present invention, free oxygen-containing gas in injected through the oxygen injection well. This free oxygen-containing gas is injected in an amount within the range from about 500 to about 1500 cubic feet of free oxygen per ton of oil shale which is subjected to combustion. The free oxygen-containing gas may be air or other free oxygen-containing gas. In some instances, it may be desirable to use substantially pure free oxygen. An amount of about 1000 cubic feet of free oxygen per ton of oil shale will give desirable results. Where air or other free oxygen-containing gas is used, a suificient amount will be employed to provide the necessary amount of free oxygen.

The free oxygen-containing gas in injected into the formation for supporting the combustion operation is injected at a sufficient velocity of allow the formation and the maintenance of a fluidized solids bed in the cavern.

hydraulic fracturing through the third 3,233,668 Patented Feb. 8, 1 966 The free oxygen-containing gas is injected at a suflicient velocity to provide a superficial gas velocity in the cavern within the range from about 0.1 to about 2.5 feet per second. A preferred superficial gas velocity is within the range from about 0.3 to about 0.6 feet per second.

Superficial gas velocities above about 2.5 feet per second should not be employe since between about 2.5 and about 4.0 feet per second of the shale fines, which result from burning the shale formation and by attrition in the fluidized bed, may be blown from the cavern which is undesirable and must be controlled. Above about 4 feet per second, the fines will be substantially lost from the cavern and the bed will not be formed.

When free oxygen is employed in the practice of the present invention, it may suitably be produced by electrolysis of water under an elevated pressure within the range from about 1000 to about 3000 p.s.i.g. Electrolysis under pressure produces ahigh pressure oxygen for the injection operation and high pressure hydrogen for subsequent treatment of the shale oil for removal of nitro gen and sulfur. An insufficient amount of water is produced from the cavern resulting from the combustion operation for electrolysis to produce the necessary amount of oxygen and hydrogen, However, additional water will be recovered from the formation itself. It is to be understood that fresh water from an external source in addition may be used for the electrolysis operation and suitable electrolytes may be added to the water regardless of its source, as may be required. As examples only of suitable electrolytes may be mentioned solutions containing about 30 weight percent potassium hydroxide, or 30 weight percent sulfuric acid, or weight percent phosphoric acid. It is to be understood, however, that the invention is not limited to these electrolytes or concentrations.

Temperatures in the burning zone in the cavern may range from about 1000 to about 1400" F. A preferred temperature may range from about 1150 to about 1250 F., wth good results being obtained at around 1200 F.

Temperatures in the cracking zone may range from about 700 to about 1000 F. with preferred temperatures ranging from about 900 to about 950 F. A suitable temperature is 925" F.

The pressure in the cavern should be suitably controlled such that the pressure does not exceed the breakdown pressure of the formation. Thus, the pressure may depend on the depth of the cavern from the earths surface which may range from about 500 to about 4000 feet. Pressures may be controlled by throttling the output wells. Likewise, the temperatures in both the burning zone and the cracking zone may be controlled by the rate of free oxygen injection or by supplementary injection of water and/ or steam, as may be required. Another way of controlling temperatures is by return of slurry oil to the bottom of the cavern through a separate well to serve as fuel. Still another mode of temperature control is by the control of oil shale fed into the cavern by caving of the roof of the cavern.

In this respect, the caving of the roof and enlargement of the cavern is suitably obtained by progressive fracturing if the formation above the cavern at intervals within the range of about 4 to about 20 feet above the top of the cavern. This may be accomplished by well or by controlled explosions, or by explosively fracturing the formation through the third well as will be described further hereinafter.

Raw shale oil is formed and vaporized as the shale is retorted while moving downward through the fluidized bed toward the burning zone. In the burning zone, residual carbon is burned from the spent shale allowing it to disintegrate into fluidizable solids which are removed 3 from the burning zone in the fluidized state. This allows additional spent shale to move downward into the burning zone. Additional raw shale is added to the top portion of the fluidized bed as the spent shale is converted to fluidized solids in the burning zone.

The level of the fluidized bed in the cavern may be controlled by selective withdrawal of fines from the bottom of the cavern in the dense fluidized bed by providing a separate withdrawal Well or by Withdrawal of fines through the output well. The fluidized bed should be controlled at a level at least about 20 feet below the roof of the cavern and may desirably be at a level from about 20 to about 100 feet below the cavern roof.

Although slurry oil may be returned to the bottom of the cavern to serve as fuel for the burning zone, slurry oil may be returned to the top of the cavern, as may be desired, through a separate cased hole to the top of the cavern. Slurry return to either the top or the bottom of the cavern is desirable since it provides a means of returning fines entrained in the product vapors back to the underground cavern.

The shale oil as produced contains nitrogen and sulfur, usually in combined form. The shale oil as produced is therefore unsatisfactory and must be subjected to treatment for removal of nitrogen and sulfur or for converting them to an innicuous form. This is accomplished by hydrogenation of the lighter fractions of the shale oil. Conditions for hydrogenation include temperatures within the range from about 700-800 F., with a preferred temperature of about 750 F.; and pressures within the range of about 600-l000 p.s.i., with a preferred range of about 700-900 p.s.i. A suitable pressure when a temperature of about 750 F. is used is about 800 psi.

Hydrogen consumption will range from about 1000- 2000 cubic feet per barrel and a preferred catalyst is cobalt molybdate although other hydrogenation catalyst may be used.

The shale oil fraction is fed to the hydrogenation unit at a rate sufiicient to provide a space velocity Within the range from about 0.25 to about 1.0 v./v./hr.

The present invention will be further described with reference to the drawing in which:

FIG. 1 is a cross-sectional view showing the spacing of the wells for one cavern;

FIG. 1-A is a modification of FIG. 1;

FIG. 2 is a surface ground view of the well spacing for one cavern;

FIG. 3 illustrates a plurality of caverns formed in accordance with the present invention;

FIG. 4 is a flow diagram of the surface operation for recovery of shale oil from a cavern; and

FIG. 4-A is a flow diagram of the hydrogenation and electrolysis system.

Referring now to the drawing in which identical numerals will designate identical parts and particularly to FIG. 1, numeral 11 designates the earths surface from which an injection well 12, is drilled into an oil shale formation 13. Oil shale formation 13 is overlaid by formations designated as overburden 14. Second wells are spaced from the injection well 12 and these wells may be drilled vertically and then deviated so that they open adjacent the first or injection well 12. Wells 15 may be substantially vertical throughout their depth. Third wells, which are designated as fracturing wells 16, may be drilled between the first and second wells such that they open into the formation 13 adjacent and between the first well 12 and second well 15. These wells 1d may also be substantially vertical. The first well 12 and the third wells 16 may be cased throughout their length, while the second wells 15 may be cased through the overburden 14 but have an open bore in the oil shale formation 13. Since the casings of well 12 and wells 16 are subjected to high temperatures, these casings may be suitably constructed, at least throughout their length in the formation 13, of special metallic alloys or other materials which will safely withstand the high temperatures obtaining as the combustion operation proceeds. Under some conditions it may be desirable and preferable to conduct the present invention with wells which are provided only with a surface pipe but otherwise are not cased. Thus, wells 12, 15, and 16 may or may not be cased as desired.

Where the well such as 1.2 is not cased, it may be deviated and terminate in the zone 13 as shown in FIGURE 1A. In the case of wells 16 fracturing may be conducted from an open hole as desired.

The well 12 is suitably closed at the surface 11 by a wellhead 17 having attached thereto a free oxygen injection line 18. Wells 15 are connected to a manifold 19 and are controlled by valves 20, connected to wellheads 21. Wells 16 are closed by wellheads 22 to which lines 23 connect, through which fracturing fluid or explosives are injected.

In the practice of the present invention in accordance with the best mode contemplated, a cavern such as 23 is formed by explosively or hydraulically fracturing formation material 24 and by injecting free oxygen into the fractured formation material 24- through the casing 12 provided with perforations 25. A burning zone 26 is then initiated in the cavern 23 which assists in the formation of the cavern and forms a fluidized bed 27 above the burning zone 26. Mild cracking takes place in the fluidized bed, the attrited shale formation material providing heat transfer to the products undergoing cracking allowing use of relatively low cracking temperatures in the range from about 700 F. to about 1000 F. The fracturing is conducted through wells 16 by means of perforations 16a which may suitably be formed by using the Wel -known gun perforating technique. Since there are several wells which may be adjacent each other, it may be desirable to use an oriented gun to avoid perforating the other wells.

Products are withdrawn from the cavern 23 through output wells 15 and are separated and processed as described with respect to FIGS, 4 and 4-A.

Referring now to FIG. 1-A, a well 12a is drilled into the formation 13. The Well 12a has a vertical component 23 and a deviated component 29. In this modification, the deviated component 29 provides for oxygen injection into the cavern 23 without exposure of long sections of the casing to high temperatures obtaining in the burning zone and in the cracking zone. Thus, only a small portion of the well 12a need be provided with sp cial metallic alloys to resist the high temperature environments.

Referring now to FIG. 2, an areal pattern for the wells 12, 15, and 16 is shown with the several wells all having substantially vertical bores. Particular attention is directed to the spacing of the wells 15 and 16 relative to well 12.

In FIG. 3 an arrangement of the caverns 23 formed around several of the wells 12 (the wells 15 and 16 not being shown) is shown such as contemplated in the present invention. Referring to FIG. 3, wherein the wells are all drilled substantially vertically, it will be seen that the spaces 30 between the walls form supporting pillars for the formation. Also, the spaces 30 may suitably be denuded of shale oil content by heat transfer from two or more caverns as the caverns are gradually formed and enlarged to have the diameters mentioned before and shown in the drawing. In this manner, the temperature of the spaces 30 between the caverns will, after a period of time from about 5 to about months, approach the temperatures obtaining in the caverns, allowing substantial recovery of the oil from the shale. By virtue of the fact that a burning operation takes place only in the caverns, the formation material in the roofs of the caverns and in the walls of the caverns may be denuded of 011 but is not weakened by combustion, thus retaining its strength and serving to maintain the caverns without sloughing of the walls or the roof except by intentional 5. caving of the roof by the fracturing technique. Where the wells 12, 15, and 16 have substantially vertical bores, as illustrated relative to FIGS. 2 and 3, the caverns formed are generally of cylindrical shape.

Referring now to FIG. 4, there is shown a substantially cylindrical cavern, such as 23, provided with an outlet well 15 connected to a manifold 19 for recovery of products. The manifold 19 connects to -a cooling means 31 for reduction of temperature of the combustion prodnets and shale oil. The cooled products are discharged by line 32 into a separating means, such as a separation zone 33 wherein an oil slurry of fines, discharged through well 15 is recovered. This oil slurry of fines, amounting to about -10% by volume of the products, may be withdrawn by line 34 and returned to the cavern 23, either to the top of the cavern by line 35, or to the bottom of the cavern by line 36, or both. The vaporous products from zone 33 are withdrawn by line 37, cooled and condensed in cooler-condenser 38 and then discharged by'line 39 into a second separation zone 40 from whence water is withdrawn by line 41 for discharge or for electrolysis. Unoondensed material, including steam, carbon dioxide and light hydrocarbons are withdrawn by line 42 and suitably may be used as a fuel for supplying heat'.

Shale oil is withdrawn by line 43 and introduced thereby into an atmospheric distillation tower 44 which is provided with suitable internal vapor-liquid contacting means or packing, such as hell cap trays and the like. Atmosphe'ric tower 44 is operated at a suitable temperature by heating means (not shown) to allow withdrawal by line 45 of a fraction boiling up to about 700 F. A bottoms fraction is withdrawn by line 46 and introduced into a vacuum distillation tower 47 which is operated under conditions to produce an overhead product which is withdrawn by line 48 com-prising hydrocarbonaceous material boiling from about 700 F. up to 90-95% of the fraction charged to tower 44. The overhead fraction in lines 45 and 48 are commingled in line 49 for further treatment as will be described. A bottoms fraction, which may be as much as 5-10% of the fraction introduced by line 43, is withdrawn by line 59 and may serve asasuitable fuel oil.

The fraction in line 49 is introduced thereby into a hydrogenation zone 51 shown in FIG. 4-A. Hydrogenation zone 51 is provided with a bed 52 of hydrogenation catalyst. Products are withdrawn from zone 51 by line 53 for recovery of various hydrocarbon fractions.

Hydrogen is introduced in line 49 through line 54 from a pressure electrolysis chamber 55 provided with electrical leads 56 and 57. C'xygen, also under pressure, is withdrawn from pressure chamber 55 by line 58 for introduction by line 18 into well 12. Water and electrolyteare introduced into chamber 55 by line 59.

The present invention is quite advantageous and useful in that by the practice of the present invention it is possible to recover oil in an economical manner from oil shale formations. The oil content of the shale is about 30%. Thus, in conventional mining, about 70-90% of inorganic material must be handled. This is avoided in the present invention.

In oil shale formations having a thickness of about 5002000 feet, caverns approximately 200 feet in diameter having an initial conical cross section which assumes the shape of a vertical cylinder as it progressively forms will ultimately correspond tothe thickness of the formation.

Oil is evolved during retorting in situ and this oil is mildly cracked in a fluidized bed which is formed such that the product is removed in the vapor state. The vapors are cooled at the surface, which permits separation of slurry oil, hydrocarbonaceous material, and water from the flue gas. By electrolyzing the water under a sufiiciently high pressure, oxygen and hydrogen under a high pressure in sufficient amounts for injection into the 6 formation and hydrogenation of the shale oil are pro vided without requiring compression. Furthermore, it has been unexpectedly found that the amount of water required is about 108 pounds per barrel of oil which produces, on electrolysis, the amount of oxygen needed, as well as the amount of hydrogen required.

The fracturing operation by Way of which the cavern is enlarged may be the hydraulic fracturing technique wherein hydraulic pressure is imposed on the formation to cause fractures therein or it may involve explosive fracturing using shaped charges, liquid or solid explosives which are detonated in or in contact with the formation. If the fracturing well is cased, the fracturing operation is performed by first perforating the casing using bullet guns, shaped charges, chemicals or by mechanical cutters, and the like. If the fracturing well is not cased, the exposed formation may be subjected directly to fracturing. Alternatively, if casing is employed, it may be provided with frangible sections which may be ruptured by pressure or mechanically, or the casing may be provided with sections which are susceptible to attack by well-known chemicals such as acids and alkalies.

The nature and objects of the present invention, having been completely described and illustrated and the best mode contemplated set forth, what we wish to claim as new and useful and secure by Letters Patent is:

1. A method for recovering oil from a subsurface oil shale formation which comprises providing a first well opening into the lower portion of said formation, providing at least a second Well opening into said formation adjacent the first well, providing at least a third well opening into said formation adjacent the first and second wells, fracturing said formation through said third well adjacent the openings of said first and second wells, injecting a free oxygen-containing gas into said fractured formation and burning said fractured formation thereby forming a cavern in said fractured formation, the free oxygen-containing gas being injected through said first well at a sufficient velocity to form in said cavern a burning zone in the lower portion and a cracking zone comprising fluidized shale solids in the upper portion of said cavern whereby shale oil and combustion products are formed, and removing said shale oil and combustion products from the top ofsaid cavern through said second well.

2. A method for recovering oil from a subsurface oil shale formation which comprises providing a first well opening into the lower portion of said formation, providing at least a second well opening into said formation adjacent the first well, providing at least a third Well opening into said formation adjacent the first and second wells, fracturing said formation through said third well adjacent the openings of said first and second wells, injecting free oxygen-containing gas into said fractured formation and burning said fractured formation thereby forming a cavern in said fractured formation, the free oxygen-containing gas being injected through said first well at a sufficient velocity to form in said cavern a burning zone in the lower portion and a cracking zone comprising fluidized shale solids in the upper portion of said cavern whereby shale oil and combustion products are formed, removing said shale oil and combustion products from the top of said cavern through said second well, and supplying oil shale to said fluidized bed by further fracturing said formation above said cavern through said third well and thereby progressively enlarging said cavern in an upward direction.

3. A method for recovering oil from a sub-surface oil shale formation which comprises providing a plurality of spaced-apart first wells opening into the lower portion of said formation, said first wells being arranged on centers within the range from about 200 to about 1000 feet, providing at least a second well opening into said formation adjacent each of said first wells, providing at least a third well opening into said formation adjacent eachof 1 said first and second wells, fracturing said formation through said each of said third wells adjacent the openings of said first and second wells, injecting free oxygencontaining gas into said fractured formation and burning said fractured formation thereby forming a plurality of caverns in said fractured formation, the free oxygen-containing gas being injected through each of said first wells at a sufficient velocity to form in each of said caverns a burning zone in the lower portion and a cracking zone comprising fluidized shaie solids in the upper portion of each of said caverns whereby heat from said caverns is transferred to the wails of said caverns and shale oil and combustion products are released into said caverns, and removing said shale oil and combustion products from the top of said caverns through each of said second wells.

4. A method in accordance with claim 3 in which oil shale is supplied to the fluidized bed in each of said caverns by further fracturing said formation above each of said. caverns through said third wells and thereby progressively enlarging said caverns in an upward direction.

5. A method for recovering oil from a subsurface oil shale formation which comprises providing a first cased well opening into the lower portion of said formation, providing at least a second well having an open bore in said formation adjacent the first well, providing at least a third cased well opening into said formation adjacent and between the first and second wells, fracturing said formation through said third well adjacent the openings of said first and second wells, injecting free oxygen-containing gas into said fractured formation and burning said fractured formation thereby forming a cavern in said fractured formation, the free oxygen-containing gas being injected through said first well at a sufficient velocity to form in said cavern a burning zone in the lower portion and a cracking zone comprising fluidized shale solids in the upper portion of said cavern whereby shale oil and combustion products are formed, and. removing said shale oil and combustion products from the top of said cavern through said second well.

6. A method in accordance with claim 5 in which the first Well is substantially vertical and the second and third wells are arranged angularly relative to said first well.

i. A method in accordance with claim 5 in which the first, second, and third wells are substantially vertical and the cavern is substantially cylindrical.

8. A method for recovering oil from a subsurface oil shale formation which comprises providing a first well opening into the lower portion of said formation, providing at least a second well opening into said formation adjacent the first well, providing at least a third well opening into said formation adjacent and between the first and second wells, fracturing said formation through said third well adjacent the openings of said first and second wells, injecting free oxygen-containing gas into said fractured formation and burning said fractured formation thereby forming a cavern in said fractured formation, the free oxygen-containing gas being injected. through said first well in an amount within the range from about 500 to about 1500 cubic feet of free oxygen per ton of oil shale at a sufficient velocity to form in the upper portion of said cavern a cracking zone comprising a fluidized bed of shale solids in which a superficial gas velocity within the range from about 0.1 to about 2.5 feet per second is maintained and wherein a burning zone at a temperature within the range from about 1000 to about 1400 F. is provided in the lower portion, said cracking zone being at a temperature within the range from about 700 to about 1000 F. whereby shale oil and combustion products are formed, and removing said. shale oil and combustion products from the top of said cavern through said second well.

9. A method in accordance with claim 8 in which a plurality of first wells are provided on centers within the range from about 200 to about 1000 feet.

10. A method for recovering oil from a subsurface oil shale formation which comprises providing a first well opening into the lower portion of said formation, providing at least a second well opening into said. formation adjacent the first well, providing at least a third well opening into said formation adjacent and between the first and second wells, fracturing said formation through said third well adjacent the openings of said first and second. wells, injecting free oxygen into said fractured formation and burning said fractured formation thereby forming a cavern in said fractured formation, the free oxygen being injected through said first well at a sufficient velocity to form in the upper portion of said cavern a cracking zone comprising a fluidized bed of shale solids and wherein a burning zone is provided in the lower portion whereby shale oil and. combustion products are formed, removing said shale oil and combustion products in vaporous form together with entrained fines from the top of said cavern through said second well, cooling said vaporous products and separating said fines in an oil slurry, further cooling said products to form a gas phase, an oil phase, and an aqueous phase and. separating said phases, subjecting at least a fraction of said oil phase to hydrogenation to remove nitrogen and sulfur, subjecting said aqueous phase to high pressure electrolysis to form free oxygen and hydrogen, and employing said free oxygen for injection into said first well and said hydrogen for said hydrogenation. v

11. A method in accordance with claim 10 in which the slurry is returned to the bottom of the cavern in said burning zone.

12. A method in accordance with claim it) in which the slurry is returned to the top of said cavern in said cracking zone.

13. A method in accordance with claim 10 in which the water is subjected to electrolysis under a sufficiently high pressure for injection into said first well.

14. A method for recovering oil from a subsurface oil shale formation which comprises providing a first well openin' into the iower portion of said formation, providing at least a second well opening into said formation adjacent the first well, providing at least a third well opening into said formation adjacent and between the first and second wells, fracturing said formation through said third well adjacent the openings of said first and second wells, injecting free oxygen-containing gas into said fractured formation and burning said fractured formation thereby forming a cavern in said fractured formation, the free oxygen-containing gas being injected through said first well at a sufficient velocity to form in the upper portion of said cavern a cracking zone comprising a fluidized bed of shale solids and wherein a burning zone is pro vided in the lower portion whereby shale oil and combustion products are formed, removing said shale oil and combustion products in vaporous form together with entrained fines from the top of said cavern through said second well, cooling said vaporous products and separating said fines in an oil slurry, further cooling said products to form a gas phase, an oil phase, and an aqueous phase and separating said phases, and subjecting at least a fraction of said oil phase to hydrogenation to remove nitrogen and sulfur.

15. A method for recovering oil from a subsurface oil shale formation which comprises providing a first well opening into the lower portion of said formation, providing at least a second well opening into said formation adjacent the first well, providing at least a third well opening into said formation adjacent and between the first and second wells, fracturing said formation through said third well adjacent the openings of said first and second wells, injecting free oxygen-containing gas into said fractured formation and burning said fractured formation thereby forming a cavern in said fractured formation,

the free oxygen-containing gas being injected through said first Well at a sufiicient velocity to form in the upper portion of said cavern a cracking zone comprising a fluidized bed of shale solids and wherein a burning Zone is provided in the lower portion of said cavern whereby shale oil and combustion products are formed, removing said shale oil and combustion products from the upper portion of said cavern through said second well, and removing fines from the lower portion of said cavern to control the level of said bed.

References Cited by the Examiner UNITED STATES PATENTS Rogers 166-39 X Martin 166-1l X Pevere et al. 166-11 Watson 166-11 

1. A METHOD FOR RECOVERING OIL FROM A SUBSURFACE OIL SHALE FORMATION WHICH COMPRISES PROVIDING A FIRST WELL OPENING INTO THE LOWER PORTION OF SAID FORMATION, PROVIDING AT LEAST A SECOND WELL OPENING INTO SAID FORMATION ADJACENT THE FIRST WELL, PROVIDING AT LEAST A THIRD WELL OPENING INTO SAID FORMATION ADJACENT THE FIRST AND SECOND WELLS, FRACTURING SAID FORMATION THROUGH SAID THIRD WELL ADJACENT THE OPENINGS OF SAID FIRST AN D SECOND WELLS, INJECTING A FREE OXYGEN-CONTAINING GAS INTO SAID FRACTURED FORMATION AND BURNING SAID FRACTURED FORMATION THEREBY FORMING A CAVERN IN SAID FRACTURED FORMATION, THE FREE OXYGEN-CONTAINING GAS BEING INJECTED THROUGH SAID FIRST WELL AT A SUFFICIENT VELOCITY TO FORM IN SAID CAVERN A BURNING ZONE IN THE LOWER PORTION AND A CRACKING ZONE COMPRISING FLUIDIZED SHALE SOLIDS IN THE UPPER PORTION OF SAID CAVERN WHEREBY SHALE OIL AND COMBUSTION PRODUCTS ARE FORMED, AND REMOVING SAID SHALE OIL AND COMBUSTION PRODUCTS FROM THE TOP OF SAID CAVERN THROUGH SAID SECOND WELL. 